This invention relates to a mechanism for minute movement of a head capable of reading and or writing data, and more particularly to a head moving mechanism for making minute adjustments in the position of a head for magnetically or optically reading from or writing to a data storage media comprising one or more rotating disks.
Data storage devices employing one or more rotating disks with one or more surfaces on each disk useable for storing digital data are well known. Such data storage devices are often referred to as disk drives. Disk drives provide a relatively low cost means for randomly storing and accessing data. Typically, each data storage surface is divided into a number of concentric circular data tracks. Each data track is typically further divided into a number of data track locations or sectors capable of storing information. Generally, data is written or accessed by positioning a read/write magnetic head held by a head suspension for supporting the head over a selected data track while the disk is rotating. The read/write head can then read or write data to or from track sectors located on that data track. The read/write head is typically biased against the surface of the disk such that, as the disk rotates, the read/write head xe2x80x9cfliesxe2x80x9d on an air bearing above the disk.
A typical suspension system in a hard disk drive includes a voice coil motor configured for rotating the actuator arm over the desired location on the disk by rotating an actuator arm around an axis on a support spindle. A head suspension or load beam is coupled to the end of the actuator arm, and frequently, a flexure is coupled to the end of the load beam and carries the read/write head. This type of suspension is typically used in both magnetic and non-magnetic disks.
As efforts to continue to increase track density, the radial spacing between concentric data tracks on the disks decreases. As the density increases, it is increasingly difficult for known motor servo systems to quickly and precisely position the read/write head over a desired data track. Current conventional actuator-motors, such as voice coil motors, lack sufficient resolution to effectively accommodate current high track density disks. This problem is complicated by the increased susceptibility of such drives to sources of read/write errors. For example, errors can arise when the read/write head and the data tracks are offset due to a difference in coefficient of thermal expansion between respective component parts when there occurs a temperature difference between the points of time of writing and reading data. A similar offset takes place due to uneven temperature distribution during operation. These problems have necessitated the addition of a high resolution head microactuator to the conventional head positioning apparatus.
Various microactuator designs have been proposed to accomplish high resolution head positioning, including pizoelectric, electromagnetic, electrostatic, capacitive, fluidic, and thermal actuators. However, previous microactuators have not been fully successful because the proposed solutions either do not provide sufficient resolution or accuracy, or the solutions are complicated and expensive to manufacture.
What is needed is a microactuator that is relatively simple and inexpensive to fabricate, and that is capable of quickly and accurately positioning a head over a desired data track.
Accordingly, the current invention is a head positioning assembly or microactuator that is lightweight, inexpensive to manufacture, and that provides the desired resolution or track positioning accuracy. The microactuator of the invention comprises a slider support arm with a slider positioned on the slider support arm to read from or write to a data medium. An anchor structure is spaced apart from the slider support arm to define a gap separating the slider support arm and the anchor structure. A piezoelectric element is coupled at one end to the slider support arm, and at the other end to the anchor structure, with the middle portion of the piezoelectric element extending across the gap separating the slider support arm and the anchor structure.
The head positioning assembly of the invention is preferably formed as an integral structure by cutting a gap in the distal end of the load beam (the end furthest from the servo motor) to separate the slider support arm and the anchor structure. However, in alternate embodiments, the microactuator may comprise separate elements that are coupled to the load beam, or the microactuator may be coupled to or formed on a flexure coupled to the load beam. In some embodiments, the slider support arm may include a means for reducing the vertical motion of the slider support arm in a direction approximately perpendicular to the surface of the data storage medium.
In a preferred embodiment, the piezoelectric element is affixed to the slider support arm and to the anchor structure by a resin adhesive. Any piezoelectric element may be useable in the invention, however, a multi-layered or laminate PZT (lead zirconate titanate) piezoelectric element is preferred.
Conductors are placed in electrical contact with the piezoelectric element so that a voltage differential between the conductors will cause a change in geometry of the piezoelectric element. The piezoelectric material is fabricated and positioned, as is well known, so that a voltage differential of a selected polarity will cause a geometric change in configuration of the piezoelectric element causing the piezoelectric element to lengthen. A voltage differential of a reverse polarity will cause an opposite shortening of the piezoelectric element. The change in length of the piezoelectric element causes the slider support arm to move relative to anchor structure, allowing the fine control of the position of the slider over a selected data track.
In the preferred embodiment the flexible slider support arm is bent by the movement of the piezoelectric element in order to position the slider. However, in alternate embodiments one or more hinge structures may be formed on or coupled to the slider support arm so that the slider support arm will tend to bend or pivot only at the hinge structure.